1. Field of the Invention
This invention relates to video cameras, more particularly, to a process of forming fiducial marks on an imaging surface of a video tube, and the use of the video tubes so marked.
2. Description of the Prior Art
In general, video cameras are used to make geometric measurements, and in particular at Naval Weapons Center, China Lake, Calif., video cameras have been used for many years for weapons impact scoring, fuse function measurements, miss distance, velocity measurements and trajectory measurements, but the poor geometric properties of the tube type video imagers have been a problem. Usually, several markers are needed in the field of view to give scale and usually it is not practical to have enough markers to make non-linearity corrections. Also, it is common that some marker is needed to designate target center.
Video cameras using solid state imagers have also been used to measure weapons impact and fuse scoring. Geometry and scale are essentially perfect, but the cameras have much poorer resolution, less automatic light control range, noise at high temperatures, poor external sync locking, poor blooming characteristics (low blooming threshold and coulomb blooming) and higher production expenses. The overall advantage of using the present generation of commercially available solid state cameras versus tube imager cameras for weapons impact and fuse scoring is doubtfull as to the present intended purpose.
One prior process of forming fiducial marks on video tubes used a mechanical scribing device. This process had to be accomplished only during manufacturing of the tubes. This failed to satisfy customer requirements as to particular markings required, and further committed the video tubes so marked to that use without knowing customer demands. Tailoring manufacturing to customer requirements and demands is not economical. A process of marking video tubes already possessed by customers removes these manufacturing detractors.
Additionally, mechanical scribing of the imaging surface has resulted in fiducial marks of low quality; lacking sharpness and accuracy in position.
Further, video tube imagers lack linearity and the scale of the image produced is variable across the field of view. A process to compensate for this lack by placing fiducial marks on the imaging surface for compensation is needed.
Other processes for placing fiducial marks on images formed by video tubes is by electronic insertion or by using film with marks. Both of these techniques fail to compensate for geometric distortion caused by video tubes or for inadequacy of determining the true geometric scale of the video tubes. Both require additional expenses such as purchasing high cost video cameras with better linearity and scale characteristics.